Double Dovetail Puzzle, Optical Illusion or Real Creation?

Crossposted from Optical Illusions Etc...

The below item is composed of two solid pieces of wood. There are no holes in this block. If you grab the top piece and lift the bottom comes with it. I first saw this as the Visual Illusion of the month on Amos Storkey's site.

The top picture was pointed out to me by Rob of "What is it?" Rob's site has an array of pictures with the object being to guess what the object is in the picture.

All Rob has to say about this object is that it is the
Double dovetail puzzle

Amos presented the bottom picture with the following statement:

A craftsman took two solid pieces of wood, and carved them so they could be put together in the form illustrated below (the slight overhang is only used to illustrate the two parts). Each part is solid, and cannot be separated. The whole block is solid and has no spaces inside. The full cube could be lifted by picking up the top half.

How was this cube created (no adhesive used)?

I have pondered this puzzle since I saw it on Amos' site. It wasn't until today when Rob of What is it? dropped me an e-mail did I decide to put some serious thought to this puzzle.

It took me a couple of minutes of thought then the answer hit me. I love this kind of puzzle. It works because we always make assumptions, it isn't until you throw those assumptions away that the answer reaches out and smacks you in the face.

Once the solution came to me I decided to include the photo from Amos' site . The bottom photo is a blatant clue on how this puzzle is done. You might as well show the construction blueprint.

Let's see who is the first person to comment correctly on this puzzle.

Good luck!